I'm using a 3 router AXE5300 (bought from Costco) with an additional XE75 router.  I had everything set up nicely (main deco connected to modem, 3 other routers connected through ethernet backhaul) with no issues for around 6 months.  Suddenly, I lose Internet on my wifi network.  I end up swapping out an ethernet cable and get internet back up and running.  However, now some devices have issues connecting.  I have been working on this for the past 8 hours now, resetting and trying to add the decos back to the system.  However, even though all of the routers are connecting and "working," the mapping is completely wrong.  Here's what I had before:

Main Deco   > Living Room (ethernet)

                    > Guest Room (ethernet)

                    > Office (ethernet)

Basically, each router branched off directly from the main deco.  But now, I am only seenig the following:

Main Deco > Office (wifi) > Guest Room (ethernet)

                                        > Living Room (ethernet)

So now, the Guest Room and Living Room branch off from the Office Deco, which claims it's connected via wifi.  Everything is routed as it was before.  Modem > Main Deco > Ethernet Swith (TP Link TL-SG608) > Other Decos & Devices

What's going on here?  I've even disconnected the Office from ethernet, then I lose connection to my other Decos.